1. Field of the Invention
The invention relates to an electrically conductive floor covering.
2. Description of Related Art
Static charges which are produced by walking or traveling on plastic floor coverings, particularly at low atmospheric humidity, represent a serious problem, particularly for sensitive electronic components. The electronic components may be damaged or their function may be impaired by electrostatic discharges. Furthermore, in areas in which easily flammable materials are worked with, there is the danger that these materials will be ignited by spark-over in the event of static discharges. The avoidance of static charges is particularly important in surroundings which are air-conditioned and therefore have a low atmospheric humidity, such as computer centers, manufacturing facilities for electronic components and electronic devices, radiological facilities, operating rooms, and other areas in which care is taken to provide an atmosphere low in dust and particles.
The floor coverings typically used, for example those based on polyvinyl chloride or rubber mixtures, are insulators. They may be made conductive if conductive fillers or antistatic agents are mixed in. However, a relatively large quantity, typically between 30 and 50 volume-percent of a conductive filler, must be used to achieve a sufficient conductivity. Metallic materials, conductive carbon black, or graphite are used in particular as conductive fillers, but the use of the necessary quantities results in black or gray products. If antistatic agents are used, there is the disadvantage that these materials react very strongly to changes in atmospheric humidity and their effectiveness is therefore strongly dependent on the environmental conditions.
A method for producing highly compressed, conductive covering material from thermoplastic plastics is known from European Patent A 869 217, in which particles of the thermoplastic plastic, which are provided with a coating containing a conductive substance, are compressed under elevated temperature and high pressure into a block with conductive paths and subsequently split transversely to the direction of the conductive paths into slabs of the desired thickness, with these slabs having conductive paths in the direction of their thickness. In this way, light-colored, conductive floor coverings made of thermoplastic plastic are obtained.
It is an object of the invention to provide an electrically conductive floor covering which contains a maximum of 3 weight-percent of conductive substances.
These and other objects of the invention are achieved by an electrically conductive floor covering in which the first particles comprise at least one granulated elastomer material and form a matrix in which the second particles form electrically conductive paths along the particle boundaries of the first particles.
The floor covering according to the invention allows the production of floor coverings with an irregular pattern, which has the conductive paths cut during production. The electrically conductive elastomer floor covering according to the present invention has an electric volume resistance measured according to IEC 61340 in the range from 105 to 107 xcexa9. Furthermore, the electrically conductive elastomer floor covering according to the present invention features a surface quality which corresponds to electrically non-conductive elastomer floor coverings.
The electrically conductive elastomer floor covering is preferably one in which the granulated particles pass through sieves with a mesh size between 2 to 8 mm. The conductivity of the final product can be set via the size of the granulated particles and thus by the number of conductive paths per unit area.
The electrically conductive elastomer floor covering contains substances such as carbon black, graphite, metal powder, or conductively doped mineral materials with a grain size  less than 15 xcexcm as the electrically conductive second particles.
An electrically conductive elastomer floor covering which contains conductive doped mineral fillers such as mica coated with antimony-doped tin oxide is particularly preferred. This embodiment allows the formation of colored conductive paths depending on the pigmentation, in contrast to the black conductive paths if carbon black or graphite is used.
An electrically conductive elastomer floor covering which contains 0.05 to 0.8 weight-percent of the electrically conductive second particles is particularly preferred. In spite of this very low content of conductive substances, electrically conductive elastomer floor coverings are thus obtained which have an electrical volume resistance in the range desired by the user.
Therefore, electrically conductive elastomer floor coverings are possible, having black conductive paths if carbon black or graphite is used or having colored conductive paths if coated mica is used, as are dark colored elastomer floor coverings, in which the conductive paths are set off by color for optical reasons through the use of the coated mica and appropriate pigments.
The electrically conductive elastomer floor covering according to the present invention is produced in that
a) one or more unvulcanized elastomer mixtures are granulated,
b) granulated particles which pass through sieves having a mesh width of 2 to 8 mm are coated with conductive substances,
c) put in a mold and compressed and cross-linked in a first compression procedure at a specific pressure of 5 to 200 bar and a temperature of 60xc2x0 to 120xc2x0 C.,
d) split into strips or slabs, and
e) vulcanized in a second compression procedure.
The method according to the present invention allows the production of electrically conductive elastomer floor coverings whose surface properties are comparable with those of electrically non-conductive elastomer floor coverings.
The production of the electrically conductive elastomer floor covering preferably occurs in such a way that the conductive substances are tumbled onto the granulated particles. This method allows effective covering of the granulated particles with conductive substances, through which the conductivity of the final product required by the user is achieved with a low use of conductive substances.
The conductive substances are preferably applied in the form of a bonding agent dispersion. In this way, problems with dust can be avoided and, the mechanical strength properties of the final product can be improved. In particular, an aqueous latex bonding agent is preferably used for this purpose. The use of a latex bonding agent reduces the outlay for safety arrangements and the corresponding environmental impacts because organic solvents are not used.
Multicolored, patterned, or wedge-shaped striped granulated particles are advantageously used in statistically uniform distribution. In particular light-colored granulated particles are preferably used in this case.
The vulcanization in the second compression procedure advantageously occurs at a temperature of 150xc2x0 to 190xc2x0 C. and a specific pressure of 100 to 250 bar for a period of 2 to 10 minutes. The vulcanization performed under these conditions results in a final product whose surface properties are comparable with those of typical non-conductive elastomer floor coverings.
The present invention will be described in more detail in the following with reference to two examples and a comparative example.